But not everyone in Weehawken works or shops exclusively in NYC.

The light rail wasn't intended simply to provide a connection to transit to NYC. It also improved transit connectivity within Hudson County (+ maybe Bergen county at some point) as an alternative to the traffic clogged streets.

I know people who live in Port Imperial and take the light rail to work in downtown Jersey City. Such a commute would not be as attractive without the light rail. A bus would likely be slower and less reliable without a dedicated right of way like the light rail has.